The term "standard resistance" or "standard running resistance" is herein used to mean any force which opposes the motion of an automotive vehicle which is driven to keep rolling over the surface of a flat road having 0% gradient at a constant vehicle speed. The term "running resistance" is herein used to mean any force that opposes the motion of an automotive vehicle which is driven to keep rolling over the surface of a road at a constant vehicle speed. Running resistance is equal to standard resistance if an automotive vehicle is driven to keep rolling over the surface of a flat road having 0% gradient at a constant vehicle speed. Running resistance increases and becomes greater than standard resistance if the automotive vehicle is accelerated to increase speed from the constant vehicle speed. The term "acceleration resistance" is herein used to mean this increment or difference in running resistance that has occurred due to acceleration. Running resistance is greater when the automotive vehicle is driven to keep rolling over the surface of a flat road having gradient greater than 0% at a constant vehicle speed than standard resistance for the same vehicle speed. The term "gradient resistance" is used to mean this increment or difference in running resistance.
On an ascending road, running resistance that opposes the motion of an automotive vehicle increases due to road gradient, so that the vehicle operator would feel a lack of acceleration if driving force for a flat road having 0% gradient were kept. Accordingly, the operator manipulates an accelerator pedal to cause a power train including an internal combustion engine and an automatic transmission to increase its driving force.
JP-A 9-242862 and JP-A 9-287502 disclose driving force control systems that estimate road gradient and cause a power train to alter its driving force in response to the estimated road gradient.
JP-A 9-242862 teaches selecting appropriate one of different ratio change patterns of an automatic transmission in response to road gradient for timely adjustment to an increase in running resistance caused by the road gradient.
JP-A 9-287502 teaches varying an increase in target engine torque in proportion to an increase in running resistance over the whole variation of the increase in running resistance.
The above-mentioned driving force control systems are satisfactory to some extent. However, a need remains to develop a driving force control system in such a direction as to determine a correction in amount of driving force in response to operator demand on the motion of an automotive vehicle relative to the surface of an ascending road as well as an increase in running resistance due to the road gradient.
An object of the present invention is to provide a driving force control for an automotive vehicle, which provides a good ride feel to meet operator demand on the motion of an automotive vehicle relative to the surface of an ascending road.